ROME (AFP) - The mobster father of British celebrity chef Nigella Lawson's two assistants, who were acquitted at a high-profile fraud trial in London last month, has been arrested for allegedly extorting nightclubs in Milan.

Michele Grillo, 66, previously served 15 years in prison for a kidnapping in the 1980s by the 'Ndrangheta organised crime syndicate but claimed he had changed his ways and was now working honestly as a truck driver.

Prosecutors who ordered his arrest on Wednesday said he is in fact the right-hand man of Agostino Catanzariti, who was also detained and is alleged to be the ring-leader of the group taking protection money from some of Milan's top clubs.

"In this particular case the link between business owners and 'Ndrangheta goes back a decade with a sort of 'insurance' that was periodically renewed," Paolo Storari, a prosecutor in charge of the investigation, was quoted as saying.

Police wiretaps of phone conversations between Grillo and Catanzariti have also led to the re-opening of an investigation into a murder in 1976, prosecutors said.

Grillo's two daughters, Elisabetta and Francesca Grillo, worked for Ms Lawson and her ex-husband, the millionaire art collector Charles Saatchi.

They were cleared of defrauding the couple at a trial in which they alleged Ms Lawson let them spend lavishly on designer handbags, first-class flights and other luxuries in exchange for keeping quiet about her drug use.